1. Field of the Invention
The present invention pertains to the art of crankshaft assemblies, and more particularly, to a crankshaft assembly for a motor vehicle.
2. Discussion of the Prior Art
Since the invention of the internal combustion engine over 100 years ago, nearly all crankshafts have been one piece, whether cast, forged, or machined from billets, whether for model airplane engines or huge diesels for ship propulsion or power generation. Connecting rods for the crank pins of these crankshafts had to be split or made of two pieces to allow assembly onto the crankshaft. In a minority of engines it was advantageous to utilize one piece connecting rods, thus requiring a multi-piece (assembled) built up crankshaft. The crankpin end of the connecting rod is slid onto the crankpin, and the crankpin then assembled to the flanges of the crankshaft. In smaller engines, perhaps under about 2″ stroke, a simple “press fit” assembly method works satisfactorily. On engines with greater strokes, the problem with an assembled (as opposed to a one piece or integral) crankshaft is that the flanges can rotate around the crankpin, thus losing the required perfect alignment of both flanges with each other. Misalignment results in excess vibration and the crankshaft becoming unbalanced, which causes more vibration. When a flange rotates past a certain point on the crankpin, the crankshaft assembly breaks apart catastrophically and the entire engine is destroyed.
There have been numerous attempts to overcome the problem of the flywheels shifting or twisting on the crankpin that connects them. For example, some practitioners in the market today weld the crankpin to the crankshaft flanges to try to prevent rotation of the flange(s) about the crankpin. However, this makes it impossible to disassemble the crankshaft to renew the crankpin bearings.
In an attempt to overcome unsatisfactory mechanical solutions to the problem of flywheel shifting, Harley-Davidson Motor Company developed a specific coating for the ends of the crankpin to increase the friction between the crankpin and the flywheel flange it was pressed into, as set forth in U.S. Pat. No. 7,418,939 issued in 2008. This solution has since been incorporated into production engines, indicating that the earlier attempts to solve the problem of shifting were less than 100% successful. However, this method requires an additional manufacturing step of applying a coating of friction enhancer to a crank pin, adding to the cost and complexity of manufacturing.
Therefore, there is seen to be a need in the art for a new crankshaft assembly that resists undesirable rotation around the crankpin.